1. Field of Invention
The present invention relates to digital camera modules used in digital equipment and mobile phones, and in particular to actuators for shutter and aperture control to allow miniaturized zoom modules.
2. Description of Related Art
Today there are various types of actuators used to perform shutter and aperture functions. In traditional digital still cameras where there is a focal-plane implementation with moving shutter/aperture actuators, the actuators are mounted onto the lens group where the mechanics of the shutter is mounted. The electrical connection to the shutter/aperture actuators requires design solutions, which allow the electrical connections to withstand a series of movements during camera lifetime. Most commonly a flex-cable solution is used.
In addition to problems with accommodating the electrical connection, the size of the mechanical integration is growing to achieve a stable movement, which is not a problem in traditional digital still cameras as there is enough space available. However, in miniature digital camera applications, e.g. mobile phones and portable digital assistants (PDA), space is a premium. Not only must there be space allocation for a lens group, but also for a shutter motor and the electrical cable to power the shutter motor. Also motors used in present day digital cameras require considerable power, which puts a drain on the battery of miniature devices, and requires power drivers that are not easily integrated into the camera control chip.
In FR 823395 (Lavet) a low energy stepper motor is directed to horological devices such as watches and clocks. U.S. Pat. No. 5,206,983 (Guckel et al.) is directed to a micromechanical device formed on a substrate using X-ray lithography process to form a rotating micro motor which is driven magnetically.
In FIG. 1 of prior art a shutter actuator motor 10 is mechanically coupled to a shutter/iris located on the optical axis of a lens group 12. The shutter actuator is physically attached to the lens group, which requires a flexible electrical connection such as a flex cable 13 to connect electrical signals to the actuator. Over the life of the digital camera module the flex cable must withstand numerous movements of the lens group, which not only requires the flex cable to have physical properties to withstand the numerous movements but also to allow physical space to accommodate the flexing of the flex cable. Electrical signals are connected to the flex cable 13 by motor driver circuits 14, which are supplied commands from a control chip 15. The motor driver circuits cannot be easily integrated into the control chip because of the amount of current and the associated power needed to be supplied to the shutter motor of the prior art.
In the watch industry precision, compact and low power actuators have been implemented using a Lavet motor concept. The Lavet type motors are capable of driving watch mechanisms with very low voltages and consuming very low current. This is a result of the Lavet style motors being active only when a step is performed, which leads to a very low power consumption resulting in battery life up to five years. Applying the Lavet concept to actuators in motorized camera modules produces lower power consumption along with a smaller size and simple electronic control, wherein the actuator power consumption is approximately fifteen times lower with approximately ten times lower current consumption at a one and a half times lower voltage. This leads to operating product containing digital cameras longer than product using conventional actuator and is particularly important to the mobile phone market.